The present invention relates to the field of plant molecular biology, more particularly to regulation of gene expression in plants.
Expression of heterologous DNA sequences in a plant host is dependent upon the presence of an operably linked promoter that is functional within the plant host. Choice of the promoter sequence will determine when and where within the organism the heterologous DNA sequence is expressed. Where expression in specific tissues or organs is desired, tissue-preferred promoters may be used. Where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. In contrast, where continuous expression is desired throughout the cells of a plant, constitutive promoters are utilized. Additional regulatory sequences upstream and/or downstream from the core promoter sequence may be included in expression constructs of transformation vectors to bring about varying levels of expression of heterologous nucleotide sequences in a transgenic plant.
Frequently it is desirable to express a DNA sequence in particular tissues or organs of a plant. For example, increased resistance of a plant to infection by soil- and air-borne pathogens might be accomplished by genetic manipulation of the plant""s genome to comprise a tissue-preferred promoter operably linked to a heterologous pathogen-resistance gene such that pathogen-resistance proteins are produced in the desired plant tissue.
Alternatively, it might be desirable to inhibit expression of a native DNA sequence within a plant""s tissues to achieve a desired phenotype. In this case, such inhibition might be accomplished with transformation of the plant to comprise a tissue-preferred promoter operably linked to an antisense nucleotide sequence, such that expression of the antisense sequence produces an RNA transcript that interferes with translation of the iRNA of the native DNA sequence.
Thus far, the regulation of gene expression in plant roots has not been adequately studied despite the root""s importance to plant development. To some degree this is attributable to a lack of readily available, root-specific biochemical functions whose genes may be cloned, studied, and manipulated. Genetically altering plants through the use of genetic engineering techniques and thus producing a plant with useful traits requires the availability of a variety of promoters. An accumulation of promoters would enable the investigator to design recombinant DNA molecules that are capable of being expressed at desired levels and cellular locales. Therefore, a collection of tissue-preferred promoters would allow for a new trait to be expressed in the desired tissue.
Thus, isolation and characterization of tissue-preferred, particularly root-preferred, promoters that can serve as regulatory regions for expression of heterologous nucleotide sequences of interest in a tissue-preferred manner are needed for genetic manipulation of plants.
Compositions and methods for regulating expression of heterologous nucleotide sequences in a plant are provided. Compositions comprise novel promoter sequences that initiate transcription in a root-preferred manner. More particularly, a transcriptional initiation region isolated from the plant gene Knox1 is provided. Further compositions of the invention comprise the nucleotide sequence set forth in SEQ ID NO:1, a fragment of the nucleotide sequence set forth in SEQ ID NO:1 comprising at least 20 nucleotides, and the nucleotide sequence deposited as Patent Deposit No. 98917. The compositions of the invention further comprise nucleotide sequences having at least 70% identity to the sequence set forth in SEQ ID NO:1 or a fragment thereof, and nucleotide sequences that hybridized under stringent conditions to any one of the above mentioned sequences.
Compositions of the present invention also include an expression cassette comprising a promoter, operably linked to a nucleotide sequence of interest, wherein said promoter is capable of driving expression of said nucleotide sequence in a plant cell and said promoter comprises the nucleotide sequences of the present invention. The invention further provides an expression vector comprising the above mentioned expression cassette.
Compositions further include a plant or a plant cell having stably incorporated into their genomes an expression cassette comprising a promoter operably linked to a nucleotide sequence, wherein said promoter is capable driving expression of said nucleotide sequence in a plant cell and said promoter comprises a nucleotide sequence of the present invention. Additionally, compositions include the seed of such plants.
Methods of the invention comprise a means to express a nucleotide sequence in a plant, said method comprising, stably incorporating into the genome of a plant cell an expression cassette comprising a promoter operably linked to a nucleotide sequence, wherein said promoter is capable of initiating transcription of said nucleotide sequence in said plant cell and said promoter comprises a nucleotide sequence of the present invention.